The invention refers to a system and to a method for communicating the location of an emergency caller from a mobile telephone set through a telephone network to a control station which is handling the emergency call in which position data corresponding to the location of the mobile telephone set is obtained and transformed into a format to be transmitted to the control station.
According to federal regulation U.S. telephone network operators offering services for Public Answering Service Points must to provide ability to communicate the position of the calling party during an emergency call to the emergency authority, e.g. a police station. As long as the telephone set which a person in an emergency situation is calling from is connected to a wire based network, the telephone company operating the Public Answering Service Point already knows the fixed location of the calling party. In a wireless telephone network, however, the location of the calling party is not known to the networking company at sufficient accuracy. From Oct. 1, 2001 on federal regulation in the U.S. will require an accuracy of the location in the range of less than 125 meters using a root mean square methodology.
In U.S. Pat. No. 5,873,040 a wireless 911 emergency location system is disclosed where several mobile switching offices share a common database. In order to locate the caller the signal strength is measured at the base station communicating with the calling cellular phone. The measured value is passed with the switching offices to the shared computer to calculate the search area. A detailed mapping of the calculated area is provided to the emergency assistance center. The position of the caller is rather inaccurate.
European patent application no. EP-A1-0,897,119 teaches a cellular transmitter for automatically providing position location and emergency. The mobile telephone set comprises a GPS positioning device to provide the coordinates of the caller. A stored telephone number is transmitted to the switching office together with the position data.
In the co-pending U.S. patent application Ser. No. 09/022558 entitled xe2x80x9cSystem and method for communicating information through a telephone networkxe2x80x9d filed Feb. 12, 1998, a system for communicating the position of a mobile object having a cellular transceiver is disclosed. The position data is transformed into one or more of a multitude of assigned telephone numbers. The telephone numbers represent the location information to be transmitted to a switch using the xe2x80x9ccallbackxe2x80x9d or xe2x80x9cdirect Inward dialing (DID)xe2x80x9d service. The transmission of each DID is accomplished during the handshake when the calling telephone set is setting up the communication link to the switch as long as the connection is not yet fully established, which means that the switch is still xe2x80x9con hookxe2x80x9d. As a result communication charges are avoided. A set of DID telephone numbers is obtained from the telephone network operator on a rental basis for a fixed, e.g. monthly, fee.
The object of the invention is to provide a system for communicating the location of an emergency caller from a mobile telephone set through a telephone network to a control station handling the emergency call which can be easily implemented.
Another object of the invention is to provide a respective method for communicating the location of an emergency caller.
With respect to the system, the foregoing object is solved by a system for communicating the location of an emergency caller through a telephone network to a control station for handling the emergency call comprising a mobile telephone set; a location detection unit arranged in said mobile telephone set for obtaining position data of the location of said mobile telephone set: a transforming unit arranged in said mobile telephone set and coupled to said location detection unit for receiving said position data and for transforming said position data into a set of audio tones representing said position data; and a transceiving unit arranged in said mobile telephone set for transmitting said audio tones representing said position data through said telephone network when a call connection between said mobile telephone set and said control station is established;
and alternatively by a system for communicating the location of an emergency caller through a telephone network to a control station for handling the emergency call comprising a mobile telephone set; a location detection unit arranged in said mobile telephone set for obtaining position data of the location of said mobile telephone set; a transforming unit arranged in said mobile telephone set and coupled to said location detection unit for receiving said position data and for transforming said position data into one of a multitude of assigned telephone numbers representing said position data; and a transceiving unit arranged in said mobile telephone set for transmitting said one of said assigned telephone numbers through said telephone network when a call connection between said mobile telephone set and said control station is being set up.
With respect to the method, the foregoing object is solved by a method for communicating the location of an emergency caller from a mobile telephone set through a telephone network to a control station handling the emergency call comprising the steps of obtaining position data of the location of said mobile telephone set; transforming said position data into a set of audio tones representing said position data; and transmitting said audio tones representing said position data through said telephone network when a call connection between said mobile telephone set and said control station is established;
and alternatively by a method for communicating the location of an emergency caller from a mobile telephone set through a telephone network to a control station handling the emergency call comprising the steps of: obtaining position data of the location of said mobile telephone set; transforming said position data into one of a multitude of assigned telephone numbers representing said position data; and transmitting said one of said assigned telephone numbers through said telephone network when a call connection between said mobile telephone set and said control station is being set up.
In the preferred embodiment according to the first solution employing audio tones, the position data is translated into a set of DTMF tones. Each digit of the latitude and longitude of the obtained location of the mobile telephone set is converted into a DTMF tone. The tone is transmitted to the emergency authority, e.g. police station, while the call is in progress. In the event of transmission of the position data the stream of tones can be heard. However, the duration of the stream of tones is relatively short so that the interference with the voice call connection can be neglected.
The location can be captured at repetitive intervals and updated during the call connection through respective transmission of DTMF tone sequences. The receiving device located at the emergency authority requires a tone decoder that retrieves the DTMF sequence during the emergency call and translates it back to location information in the form of longitude and latitude.
In the preferred embodiment according to the second alternative solution employing telephone numbers the location is transmitted during the handshake or setup phase of the emergency call connection. When the calling party presses an emergency button or sequence of buttons, e.g. 911 in the U.S. or a corresponding number in other countries, the location of the mobile telephone set is captured and translated Into a telephone number format which is then transmitted to a switch of the network operating company. Preferably, the telephone numbers are DIDs. The switch recognizes the DID number as being reserved for an emergency call. As the DID number corresponds to a location, the emergency call can be routed to the responsible local emergency authority.
An individual DID corresponds to a predetermined area portion, all areas covering a continuous area of possible locations where emergency service is offered. An entire country can be covered by several of such continuous areas all using the same set of DID telephone numbers in parallel. The numbers are known to the central office switch which distributes the emergency call to the next local emergency authority according to the stored assignment. As an example, a set of 5,000 DIDs with each DID assigned to an area of 5 km2 covers a continuous area of 25,000 km2. Dividing the U.S. into areas of 25,000 km2 all having the same set of DIDs the whole country can be served.
Alternatively. an identification number which is uniquely identifying the cell tower that governs the communication with the mobile telephone set can be transmitted to the central office switch in addition to the DID, A set of about 2,000 DIDs is sufficient to provide an accuracy of the location information which is even better than the federal regulation requirement.
In either embodiment, an automatic location Identification (ALI) system receiving the location information maps the location into environmental data stored at the ALI system. This data is sent to the emergency authority and displayed in order to facilitate handling of the emergency call.
The location information can be obtained in any known way. Preferably, a satellite based positioning system like Global Positioning System (GPS) is arranged in the mobile telephone set which obtains longitude and latitude of the current location of the calling party. Alternatively, a known cellular triangulation method can be used or the position of the mobile telephone set can be derived from the position of the cell tower.
The invention combines already known techniques as DTMF tone generation and decoding, direct inward dialing, ALI to provide an emergency call system based on mobile phones thereby enabling a cost efficient implementation of the system.